The present application relates, according to an aspect thereof, generally to methods and apparatus for adjusting engine exhaust gas temperature in an engine including a turbine in the exhaust stream.
Modern diesel engines typically include exhaust aftertreatment systems (EATS) with one or more components such as diesel particulate filters (DPFs), diesel oxidation catalysts (DOCs), and selective catalytic reduction catalysts (SCRs). Most of the EATS components are intended to operate within particular temperature ranges. During operation at start-up or at low loads, it may be difficult to reach or maintain the temperatures necessary to activate catalysts on equipment such as DPFs, DOCs, and SCRs. Additionally, it is occasionally necessary to increase exhaust gas temperatures to well above normal operating temperatures to regenerate components such as DPFs.
One way of raising exhaust gas temperature has been to use a variable geometry turbocharger (VGT) with a turbine downstream of the engine. The VGT can be adjusted to reduce the efficiency of the turbocharger, which can result in an increase in engine exhaust temperature. VGTs, however, tend to be expensive and involve numerous moving parts that can be subject to failure.
Another technique for raising exhaust gas temperature involves the use of a discharge recirculation valve that decreases compressor efficiency without increasing pre-turbine pressures. Still further techniques include use of intake and exhaust throttles, tailpipe hydrocarbon injection, and charge air cooler (CAC) bypass valves.
It is desirable to provide a simple, inexpensive apparatus and method for adjusting exhaust gas temperature.
According to an aspect of the present invention, a turbocharger comprises a turbine comprising a scroll passage comprising at least first and second portions, a gas outlet extending axially from the scroll passage, a turbine wheel comprising one or more blades disposed in the gas outlet, and means for establishing a bypass flow between the first and second portions of the scroll passage.
According to another aspect of the present invention, a turbocharger comprises a turbine comprising a scroll passage, a gas outlet extending axially from the scroll passage, a turbine wheel comprising one or more blades disposed in the gas outlet, a nozzle ring arranged between the scroll passage and the gas outlet, the nozzle ring comprising a plurality of vanes adapted to direct a flow of gas from the scroll passage against the one or more blades of the turbine wheel in the gas outlet, and means for moving the nozzle ring relative to the scroll passage to alter the gas flow through the nozzle ring from the scroll passage toward the one or more blades of the turbine wheel.
According to another aspect of the present invention, a method for adjusting exhaust gas temperature in an engine comprising a turbine arranged to receive engine exhaust comprises causing engine exhaust gas to flow through a scroll passage of the turbine toward a gas outlet of the turbine, the scroll passage comprising at least first and second portions, and establishing a bypass flow between the first and second portions of the scroll passage.
According to yet another aspect of the present invention, a method for adjusting exhaust gas temperature in an engine comprising a turbine arranged to receive engine exhaust comprises causing engine exhaust gas to flow through a scroll passage of the turbine toward a gas outlet of the turbine, the scroll passage comprising at least first and second portions, directing the exhaust gas against one or more blades of a turbine wheel in the gas outlet of the turbine with a nozzle ring comprising a plurality of vanes arranged at a first orientation relative to the scroll passage, and moving the nozzle ring from a first position relative to the scroll passage in which the plurality of vanes on the nozzle ring direct gas against the one or more blades of the turbine wheel to a second position relative to the scroll passage in which gas flow from the scroll passage through the plurality of vanes into the gas outlet is altered relative to gas flow in the first position.